Feline calicivirus infection is a common and serious disease of cats usually associated with the respiratory tract. There has been many serotypes reported in the literature as causing from slight respiratory problems to severe pneumonia in cats. Reports in the literature indicate that this disease is responsible for approximately half the clinical cases of feline respiratory infections. The virus infects the epithelial cells of the nose, lung, pharynx, trachea and eye, causing epitheliolysis and necrosis. Resultant signs vary from inapparent infection to mild respiratory disease to severe respiratory disease with pneumonia and sometimes death. Further ulcerative lesions of the nose and tongue are often associated with the disease as are anorexia and pyrexia. The virus is shed from the nose, eyes and mouth through the course of the clinical disease. Feline calicivirus infections are often severe and complicated further by bacteria when resistance becomes low. Mortality may be significant, especially in young kittens. The transmission of feline calicivirus to susceptible cats is generally by intranasal instillation, for example, by droplets expelled in sneezing or by contact (usually nose to nose). Resistance following recovery from natural or experimental infection is of moderate duration.
The FCV group of serotypes was formerly called Picorna virus. This name was changed by the International Committee on viral nomenclature in 1971 designating this viral group as Picorna viradae in the genus calicivirus. The first isolation of a feline calicivirus serotype was reported by L. B. Fastier in Amer. J. Vet. Res., 18, 382 (1957). Since then, several reports have appeared in the literature which confirm the isolation of feline calicivirus from feline subjects in various parts of the world which identify the virus as a feline member of calicivirus, and which describe the transmission, epidemiology and histologic characteristics of the disease, as well as the infections observed from different serotypes. For example, see J. L. Bittle et al., Amer. J. Vet. Res., 21, 547 (1960) and 22, 374 (1961); F. Burki, Arch. F. die Gesam. Vir., 15, 690 (1965); R. A. Crandall, Proc. Soc. Exptl. Biol. & Med. 126, 240 (1967); Kahn & Gillespie, Cornell Vet., 60, 669 (1970); Holzinger & Kahn, Amer. J. Vet. Res., 31, 1623 (1970); and E. Takahashi et al., Jap. J. Vet. Sci., 33, 81 (1971).
An excellent up-to-date review is provided by Gillespie and Scott in the book, "Advances in Veterinary Science and Comparative Medicine," Volume 17, Edtd. by C. A. Brandly and C. E. Cornelius, pages 176-188, Academic Press, Inc., New York, 1973. Previous attempts at immunization with feline calicivirus are termed impractical by Gillespie & Scott (page 189). To date, no effective vaccine is available for protecting cats against feline calicivirus.